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I am looking to heat my garage and am wondering why I could not just use the furnace in my house and run a duct to the garage. The garage is insulated, R38 in ceiling and R11 in walls. As long as the home furnace has enough capacity is there any reason this would not work well.
I am not looking for a quick recovery when I drive in. The house I grew up in had a garage heated this way and it seemd to work fine.

You shouldn't tie your house system into the garage. Think about the fumes/carbon monoxide that you generate in the garage and having them circulate through out the house. Then there is the breach of the fire wall between the house/garage and the fire path that will be provided by the duct work.

Ray

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Knowledge is knowing that F=ma. Wisdom is knowing why that is important.

I am not sure I understand. We don't run our vehicles with the garage door shut and the furnace would not suck air out of the garage and push it into the house. How realistic is it that a harmful amount of fumes would ever enter the house? Have you ever heard of this happening?
The fire wall safety breach is another matter. I could be convinced that the firewall code is just overkill by government safety freaks.

How much work do you do in the garage? Any parts cleaning, brake work with spray chemicals? How about chemical storage (parts cleaners/paint/etc.) Any pesticides/fertilizers/herbicides etc.? Storage of gasoline? Lawn mower, weed-eaters, chainsaws. It's not just a harmful level of fumes, but do you want the odor circulating through the whole house?

If all you do is park your cars there, probably no problem. But, if you do any type of repair etc., I wouldn't tie into the system.

There is also a possibility that you might have trouble with your homeowners insurance in event of a fire. Even trouble with the sale of the house in the future if there is a home inspection required and/or a building code violation.

I just wouldn't do it.

Ray

__________________
Knowledge is knowing that F=ma. Wisdom is knowing why that is important.

Ray-CA sums it up best!
Fire Reasons, The duct work would act as a chase for fire. Think about it your garage has probaby 5/8" sheetrock and a door (metal) or fire rated to the living area. Duct work from the living space cuts the time down IF a fire were to break out (god forbid). Also any oil gas or whatever we store in the garage would permeate through the duct work into the living space. Just some friendy advice as others have mentioned do not go this route. I would use a sealed combustion or other type of hanging heater to heat the garage, why play with safety on your home. Just my 2cents.
Sixty4,,,,,

Any one way air dumped into the garage will cause the same amount of air to be made up from outside into the house. Even newer houses can be leaky enough to have good amounts of air draw into the house from all over. Another issue you might have is if you have natural draft gas burning devices such as the furnace or water heater. Running a negative pressure due to tight construction might cause loss of draft and combustion air to be drawn back into the house. Negative air pressure in the house is to be avoided if you can.

Not a good idea to cut into the garage. Even with a fire damper to protect in that case you might end up with a event where the garage air is pulled into the house. an upstairs window open on a cold evening can cause negative pressure in the lower flowers and fumes to be pulled backwards in from the garage.

Insurance implications are a factor as well.

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A wise man knows his ignorance. A fool thinks he knows everything.

Will it heat it yes ,,, my buddy did it it works well, does he work in his garage no just parks his car in there , id go with a propane /natural gas wall hanger heater if you plan on doing alot of work.good luck mike.

__________________Work to live not live to work.

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Mine is setup that way, it passed inspection here, for what that's worth. I have to keep it heated, my pressure tank/plumbing/washer/water softener is in there. I'm not comfortable running a separate heater in there, unless it was a second furnace, which wouldn't be practical, nor is there room for one.

I talked to a buddy who's family runs one of the local HVAC companies in the area, and he stated as long as their is not a return, there wouldn't be any issues with fumes.

He did say if the garage is tight, then w/o having a return, all you're doing is pressurizing the garage, and at some point, you will no longer be able to pump the heat into it until the pressure is changed. Think of it like blowing into a balloon.

My furnace is just inside the wall of the garage and home and I've thought about just running a quick dump into the garage, but I want to put a small exhaust fan in to help draw the air from the duct. I don't know what the code is and will check before doing so. There will definitely be a damper in there also.

Currently I am using a Big Buddy Heater w/ a 20lb tank and the condensation is killing me. Garage is finished with sheet rock, just not insulated. This would be a easy, cheap, and effective fix for my situation.

A lot of the new houses around my area are built with the water heater and furnace in the garage. Some are in a closet and some are exposed in a raised area in the corner. I'm not sure whether they are gas or electric though. Next time I go through a house being built, I'll check.

In the U.S. there are millions of homes with ductwork running from the house thru the garage , it's called a raised ranch . Many of them have the ceiling joists running from the front of the house to the back which leaves the main trunk line for heat/cool running perpendicular to them at the ceiling in the garage to feed the rooms above , many with openings in them to feed the garage. I've been in many of these homes and never really heard complaints about fumes and the homes are inspected and approved by many towns , just my 2 cents .

In your question you did not mention a return duct...In theroy, if you do not allow a way for the air in the garage to find it's way back to the furnace plenum, your heat will be ineffective. At best you will be pressurizing the garage. But in reality, garages leak enough air so that you will be able to pump heated air in there from your furnace. If you provide a return then you run the risk of admitting fumes from the garage to the house anytime the system is in operation but the feed ducting can admit fumes to the house when the system is not inoperation. As the previous reply states there are millions of houses with ducting in the garage to feed the bedrooms above and having a vent into the garage is pretty common. The systems I have seen usuallly do not have a return so remember that if you do not run a return, the air that escapes the garage as you pressurize it has to come from somewhere and that somewhere is every little place in the building that air can leak in. Unless your present furnace utilizes sealed combustion, that is to say that the combustion air is drawn fom the outdoors and exhausted thru the flue, you are admitting air to the building through every little crack anyway. This same effect also happens when you run a bath fan, clothes dryer, range hood etc. If you had a prefecty draft free house you would not be able to have these appliances work properly.

In the U.S. there are millions of homes with ductwork running from the house thru the garage , it's called a raised ranch . Many of them have the ceiling joists running from the front of the house to the back which leaves the main trunk line for heat/cool running perpendicular to them at the ceiling in the garage to feed the rooms above , many with openings in them to feed the garage. I've been in many of these homes and never really heard complaints about fumes and the homes are inspected and approved by many towns , just my 2 cents .

Yup. Thats my house.

I have 2 heated vents going in my garage. No air returns (obviously). 100,000 btu propane furnace I installed myself. Combustible and exhaust air travels through 3" pvc to outside.

Works fine...Zero fumes..(and Ive been known to paint, polyurethane, etc..) No problems. The house is 35 years old and VERY far from air tight. Maybe with a new home you'd have pressure issues. I have no idea.

This question seems to come up every few weeks, and most people seem to shout it down as being unsafe, etc.. I probably wouldnt modify my furnace to work this way (unless it was really convenient, etc). I would just buy a freestanding system. But with my house being built this way..No way Im changing it. Im thankful for it.
Now I can store stuff in the garage and not worry about it freezing, etc.
All the warm air works upwards anyways. If there were no heated vents in the garage below, the floor above would be freezing.

As far as fire traveling through the ducts..In a split level..If theres a fire in the garage..The whole house is already on fire. Really not going to matter if it travels through the ducts. Youre already toast.
I suppose it would be good practice to close the ducts during the summer (why not, I suppose).

I have 2 heated vents going in my garage. No air returns (obviously). 100,000 btu propane furnace I installed myself. Combustible and exhaust air travels through 3" pvc to outside.

Works fine...Zero fumes..(and Ive been known to paint, polyurethane, etc..) No problems. The house is 35 years old and VERY far from air tight. Maybe with a new home you'd have pressure issues. I have no idea.

Exact same deal as mine, 2 vents in garage, no return, 100,000 btu furnace, no issues. It passes inspection.

Can you Yes you can
Is it against code Yes it is .
I could go to the fun and trouble of looking up the code but I dont feel like it right now but I do know its against code .

Rick

I inquired with my home inspector, and he said that I could put in a vent and meet code. This is because the garage is finished with 5/8" fire resistant sheetrock and a 2hr burn door into the house. He also said that older homes don't have to meet the current codes (not sure what all is involved here, so this is a pretty broad statement.).

I inquired with my home inspector, and he said that I could put in a vent and meet code. This is because the garage is finished with 5/8" fire resistant sheetrock and a 2hr burn door into the house. He also said that older homes don't have to meet the current codes (not sure what all is involved here, so this is a pretty broad statement.).

Once you create any opening in a rated partition, that opening must be either fire or fire/smoke dampered or you have lost the rating. NFPA has addressed this as has the majority of Building Codes. Garages catch fire. The rated partition, separating the garage from the residential area, allows you the time to escape the building in case of fire. Chances are your house will still burn to the ground but you will be alive.

Same for the possibility of noxious or deadly fumes entering the house via ductwork that communicated with the garage.

Don't become a statistic. This is one issue that the codes have right. Even if you think you can get it past an inspector. Don't do it, if for no other reason than your HVAC System is extremely unlikely to have sufficient additional capacity to make any measurable dent in your garage temperatures.

Ok OK I went and got my code book International Residential code for one and two family dwellings section R309 garages and carports R309.1.1 Duct penetration. Ducts in the garage and ducts penetrating the walls or ceilings seperating the garage shall be constructed of a minimum No.26 gage 0.48 sheet steel or other approved material ( and shall have no openings in the garage.) There straight out of the code book question answered .

Yes you can do it NO it is not approved by code.

I will add most home inspectors dont have enough knowledge to get themselves out of an extremely wet paperbag . I have shut down more obnoxious home inspectors and their knowledge of Code than I care to remember. They dont call me The Airmedic cause I like to administer medical treatment while in Flight .

So, airmedic, what do you recommend for heating a new attached garage I am planning? My house has hot water heat fed by oil. I need a new furnace anyway, so adding size to that is not a problem. I do not have gas available either. I was thinking radiant floor heat fed by house furnace?